Systems and methods for acid recycle

ABSTRACT

Methods and systems for pretreating lignocellulosic biomass are disclosed. An acid solution between 1% to 1.6% sulfuric acid is applied to the biomass. The biomass is subjected to an elevated temperature to cause the production of xylose, glucose, and furfural. Adjustments to temperature, acid concentration, and time can generate at least 80% or 90% of theoretical xylose, 45% or 50% of the theoretical glucose, and less than 4000 ppm of furfural in the xylose liquor. A portion of the resulting xylose liquor may be separated from the glucan solids. The xylose liquor, still highly acidic, can be recycled to reduce subsequent acid loading requirements. Makeup acid solution is added to the xylose liquor and subsequent biomass to ensure a proper solids to liquids ratio. The biomass is again treated to higher temperatures to yield sugars. The process may be repeated for each subsequent cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/505,389, filed Jul. 7, 2011, and entitled “SYSTEMS AND METHODSFOR ACID RECYCLE”, the entirety of which is expressly incorporatedherein by reference.

FIELD

The subject disclosure relates to systems and methods for the recycle ofacid in a xylose stream in the production of ethanol from a cellulosicfeedstock. The subject disclosure also relates to systems and methodsfor pre-treatment of biomass before the biomass is provided to ahydrolysis system and subsequently to a fermentation system in order tofacilitate the efficient production of ethanol.

BACKGROUND

Ethanol can be produced from grain-based feedstocks (e.g. corn,sorghum/milo, barley, wheat, soybeans, etc.), from sugar (e.g. fromsugar cane, sugar beets, etc.), and from biomass (e.g. from cellulosicfeedstocks such as switchgrass, corn cobs and stover, wood, or otherplant material).

Biomass comprises plant matter that can be suitable for direct use asfuel/energy source or as a feedstock for processing into anotherbioproduct (e.g., a biofuel such as cellulosic ethanol) produced at abiorefinery (such as an ethanol plant). Biomass may comprise, forexample, corn cobs and stover (e.g., stalks and leaves) made availableduring and/or after harvesting of the corn kernels, fiber from the cornkernel, switchgrass, farm or agricultural residue, wood chips or otherwood waste, and other plant matter. In order to be used or processed,biomass is harvested and collected from the field and transported to thelocation where it is to be used or processed.

In a biorefinery configured to produce ethanol from biomass, such ascellulosic feedstocks as indicated above, ethanol is produced fromlignocellulosic material (e.g. cellulose and/or hemi-cellulose). Thebiomass is prepared so that sugars in the cellulosic material (such asglucose from the cellulose and xylose from the hemi-cellulose) can beaccessed and fermented into a fermentation product that comprisesethanol (among other things). The fermentation product is then sent to adistillation system, where the ethanol is recovered by distillation anddehydration. Other bioproducts, such as lignin and organic acids, mayalso be recovered as co-products. Determination of how to moreefficiently prepare and treat the biomass for production into ethanoldepends upon (among other things) the form and type or composition ofthe biomass.

One costly step in the preparation of lignocellulosic material forfermentation is the pretreatment of the biomass material, which requiresthe usage of a suppressed pH in order to degrade the cellulose tosugars. Typically, large doses of acid are utilized to bring the pH ofthe biomass to the levels required to effectively separate C5 sugarsfrom the C6 solids. The volume of acid required for a commercial scalecellulosic ethanol plant can be very large, which is costly to purchaseand store. Further, the large quantities of acid must be subsequentlyneutralized prior to downstream processing, such as fermentation.Neutralization is also associated with a significant cost, and mayresult in an excess of minerals, which can buildup in downstreamsystems.

SUMMARY

The disclosed aspects relate to systems and methods for pretreatinglignocellulosic biomass. The pretreated biomass may be supplied to afermentation system, or a saccharification system followed by afermentation system, for the generation of a fermentation product. Insome embodiments, the biomass may include ground corncobs, corn stover,or a combination of ground corncobs and corn stover. In someembodiments, the fermentation product may be ethanol or other bio-fuel.

In some embodiments, a method includes applying an acid solution to afirst portion of biomass. The acid solution may include between about 1%to about 1.6% sulfuric acid, in some embodiments. The biomass may besubjected to an elevated temperature for a length of time in order toyield xylose sugars in a xylose liquor and glucan solids. In someembodiments, the temperature may be maintained between about 120° C. toabout 150° C. for a period of between around 10 minutes to around 120minutes.

The elevated temperature can cause xylose, glucose, and furfural to beproduced. In an aspect, at least approximately 80% of theoretical xyloseis produced. In some embodiments, temperature, acid concentration,and/or time may be optimized (e.g., altered) to generate at least about90% of theoretical xylose. In a similar manner, the conditions (e.g.,temperature, acid concentration, and/or time) may be modified to ensurearound 45% or more (e.g., around 50%) of the theoretical glucose isgenerated. Since more severe pretreatments yield greater sugar levels,in some embodiments, the severity may be controlled such that thedesired sugar is generated without causing more than approximately 4000ppm or approximately 3000 ppm of furfural to be present in the xyloseliquor.

After the elevated temperature, at least a portion of the resultingxylose liquor may be separated from the glucan solids. The glucan solidsmay be provided to a saccharification system, in some embodiments. Insome implementations, around 70% of the xylose liquor is recovered. Inother implementations, about 75% of xylose liquor is recovered.

The xylose liquor, which can still be highly acidic, can be recycled toreduce subsequent acid loading requirements. Makeup acid solution can beadded to the xylose liquor and subsequent biomass to help ensure theproper solids to liquids ratio is met. The biomass can again be treatedto higher temperatures to yield sugars. The process may be repeated foreach subsequent cycle, according to an aspect.

DESCRIPTION OF THE DRAWINGS

In order that the disclosed aspects may be more clearly ascertained,some embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1A is a perspective view of a biorefinery comprising an ethanolproduction facility, in accordance with some embodiments;

FIG. 1B is another perspective view of a biorefinery comprising anethanol production facility, in accordance with some embodiments;

FIG. 2 is a process flow diagram illustrating the preparation ofbiomass, in accordance with some embodiments;

FIGS. 3A and 3B are process flow diagrams illustrating examples ofethanol production processes from biomass to ethanol, in accordance withsome embodiments;

FIG. 4 is an apparatus used for the preparation, pre-treatment, andseparation of lignocellulosic biomass, in accordance with someembodiments;

FIG. 5 is an example graph of the theoretical xylose concentration forxylose liquor recycles, in accordance with some embodiments;

FIG. 6 is an example graph of the theoretical acetic acid concentrationfor xylose liquor recycles, in accordance with some embodiments;

FIGS. 7-10 are example graphs of the xylose concentration in pretreatedbiomass as a function of recycle numbers for various process conditions,in accordance with some embodiments;

FIGS. 11-13 are example graphs of the glucose concentration inpretreated biomass as a function of recycle numbers for various processconditions, in accordance with some embodiments;

FIGS. 14-16 are example graphs of the acetic acid concentration inpretreated biomass as a function of recycle numbers for various processconditions, in accordance with some embodiments;

FIGS. 17-19 are example graphs of the furfural concentration inpretreated biomass as a function of recycle numbers for various processconditions, in accordance with some embodiments;

FIG. 20A and FIG. 20B list the composition of biomass comprisinglignocellulosic plant material from the corn plant according toexemplary and representative embodiments;

FIG. 21A and FIG. 22B list the composition of the liquid component ofpre-treated biomass according to exemplary and representativeembodiments;

FIG. 22A and FIG. 22B list the composition of the solids component ofpre-treated biomass according to exemplary and representativeembodiments;

FIG. 23 lists the theoretical acid and water usage for various recycleamounts according to exemplary and representative embodiments;

FIG. 24 lists the experimental conditions for a number of acid recycleexamples according to exemplary and representative embodiments; and

FIG. 25 lists the results for xylose, glucose, and furfural of theexample recycle conditions of FIG. 24 according to exemplary andrepresentative embodiments.

DESCRIPTION OF THE EMBODIMENTS

Various aspects will now be described with reference to severalembodiments thereof as illustrated in the accompanying drawings. In thefollowing description, numerous specific details are set forth in orderto provide a thorough understanding of embodiments of the variousaspects. It will be apparent, however, to one skilled in the art, thatembodiments may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe one or more aspects. The features and advantages of embodiments maybe better understood with reference to the drawings and discussions thatfollow.

Aspects disclosed herein relate to systems and methods for acid recyclein a cellulosic acid pretreatment for the generation of ethanol. Suchsystems and methods can provide cost effective means for decreasing acidand water consumption in a cellulosic ethanol biorefinery whilemaintaining xylose and glucose yields. For example, provided are systemsand methods for pretreatment of biomass in the production of ethanolwith reduced acid requirements. Also provided are systems and methodsfor reducing the need for additional acid, water, and neutralizingagents employed during biomass pretreatment in a cellulosic ethanolbiorefinery.

Referring to FIG. 1A, an example biorefinery 100 comprising an ethanolproduction facility configured to produce ethanol from biomass is shown.The example biorefinery 100 comprises an area where biomass is deliveredand prepared to be supplied to the ethanol production facility. Thecellulosic ethanol production facility comprises apparatus forpreparation 102, pre-treatment 104, and treatment of the biomass intotreated biomass suitable for fermentation into fermentation product in afermentation system 106. The cellulosic ethanol production facilitycomprises a distillation system 108 in which the fermentation product isdistilled and dehydrated into ethanol. As shown in FIG. 1A, a wastetreatment system 110 (shown as comprising an anaerobic digester and agenerator) is included in the biorefinery 100. According to otheralternative embodiments, the waste treatment system may comprise otherequipment configured to treat, process, and recover components from thecellulosic ethanol production process, such as a solid/waste fuelboiler, anaerobic digester, aerobic digester or other biochemical orchemical reactors.

As shown in FIG. 1B, according to an exemplary embodiment, a biorefinery112 may comprise a cellulosic ethanol production facility 114 (whichproduces ethanol from lignocellulosic material and components of thecorn plant) co-located with a corn-based ethanol production facility 116(which produces ethanol from starch contained in the endosperm componentof the corn kernel). As indicated in FIG. 1B, by co-locating the twoethanol production facilities, certain plant systems may be shared, forexample, systems for dehydration, storage, denaturing, andtransportation of ethanol, energy/fuel-to-energy generation systems,plant management and control systems, and other systems. Corn fiber (acomponent of the corn kernel), which can be made available when the cornkernel is prepared for milling (e.g. by fractionation) in the corn-basedethanol production facility, may be supplied to the cellulosic ethanolproduction facility as a feedstock. Fuel or energy sources such asmethane or lignin from the cellulosic ethanol production facility may beused to supply power to either or both co-located facilities. Accordingto other alternative embodiments, a biorefinery (e.g. a cellulosicethanol production facility) may be co-located with other types ofplants and facilities, for example an electric power plant, a wastetreatment facility, a lumber mill, a paper plant, or a facility thatprocesses agricultural products.

Referring to FIG. 2, a system 200 for preparation of biomass deliveredto the biorefinery is shown. The biomass preparation system may compriseapparatus for receipt/unloading of the biomass, cleaning (e.g. removalof foreign matter), grinding (e.g. milling, reduction or densification),and transport and conveyance for processing at the plant. According toan exemplary embodiment, biomass in the form of corn cobs and stover maybe delivered to the biorefinery and stored 202 (e.g. in bales, piles orbins, etc.) and managed for use at the facility. According to anembodiment, the biomass may comprise at least about 20 to about 30percent corn cobs (by weight) with corn stover and other matter.According to other exemplary embodiments, the preparation system 204 ofthe biorefinery may be configured to prepare any of a wide variety oftypes of biomass (e.g. plant material) for treatment and processing intoethanol and other bioproducts at the plant.

Referring to FIGS. 3A and 3B, alternate embodiments of a schematicdiagram of the cellulosic ethanol production facility 300 a and 300 bare shown. According to some embodiments, biomass comprising plantmaterial from the corn plant is prepared and cleaned at a preparationsystem. After preparation, the biomass is mixed with water into a slurryand is pre-treated at a pre-treatment system 302. In the pre-treatmentsystem 302, the biomass is broken down (e.g. by hydrolysis) tofacilitate separation 304 into a liquid component (e.g. a streamcomprising the C5 sugars, known as pentose liquor) and a solidscomponent (e.g. a stream comprising cellulose from which the C6 sugarscan be made available). Pretreatment may include the addition of acidsin order to lower the pH of the biomass to promote C5 separation.According to some aspects, C5 liquor may also be recycled, asillustrated, from the C5 treatment stage in order to reduce the acid andwater levels supplied to the pretreatment system. Specific examples ofrecycle conditions, volumes, and process conditions will be providedbelow in greater detail in relation to specific examples. However, otherrecycle conditions, volumes, and process conditions could also beutilized.

The C5-sugar-containing liquid component (C5 stream or pentose liquor)may be treated in a pentose cleanup treatment system 306. From thepentose cleanup treatment system 306, a recycle stream of xylose liquormay be returned to the pre-treatment system 302 as indicated above.

The C6-sugar-containing pretreated solids component may be treated in asolids treatment system using enzyme hydrolysis 308 to generate sugars.According to an embodiment, hydrolysis (such as enzyme hydrolysis) maybe performed to access the C6 sugars in the cellulose; treatment mayalso be performed in an effort to remove lignin and othernon-fermentable components in the C6 stream (or to remove componentssuch as residual acid or acids that may be inhibitory to efficientfermentation). Enzyme hydrolysis efficiency may be increased through theaddition of an agent. Such agents may include anaerobic membranedigester effluent, clarified thin stillage, wet cake, whole stillage,other viable protein source, or combinations thereof. Details of thetreatment of the C6 solids will be described below.

In accordance with the embodiment of FIG. 3A, the treated pentose liquormay be fermented in a pentose fermentation system 310, and thefermentation product may be supplied to a pentose distillation system312 for ethanol recovery. In a similar manner, the treated solids, notincluding substantial amounts of C6 sugars, may be supplied to a hexosefermentation system 314, and the fermentation product may be supplied toa hexose distillation system 316 for ethanol recovery. The stillage fromthe distillation may be treated at a lignin separation system 318 togenerate a liquid component and a solid wet cake. The wet cake may besupplied to an Anaerobic Membrane Bioreactor (AnMBR) 320 for furthertreatment, in some embodiments.

In the alternate embodiment of FIG. 3B, the resulting treated pentoseliquor and treated solids may be combined after treatment (e.g. as aslurry) for co-fermentation in a fermentation system 322. Fermentationproduct from the fermentation system 322 is supplied to a combineddistillation system 324 where the ethanol is recovered. According to oneor more embodiments, a suitable fermenting organism (ethanologen) can beused in the fermentation system; the selection of an ethanologen may bebased on various considerations, such as the predominant types of sugarspresent in the slurry. Dehydration and/or denaturing of the ethanolproduced from the C5 stream and the C6 stream may be performed eitherseparately or in combination. As with the previously describedembodiment, the stillage from the distillation may be treated at alignin separation system 326 to generate a liquid component and a solidwet cake. The wet cake may then be supplied to an Anaerobic MembraneBioreactor (AnMBR) 328 for further treatment, in some embodiments.

During treatment of the C5 and/or C6 stream, components may be processedto recover byproducts, such as organic acids and lignin. The removedcomponents during treatment and production of ethanol from the biomassfrom either or both the C5 stream and the C6 stream (or at distillation)can be treated or processed into bioproducts or into fuel (such aslignin for a solid fuel boiler or methane produced by treatment ofresidual/removed matter such as acids and lignin in an anaerobicdigester) or recovered for use or reuse.

According to an embodiment, the biomass comprises plant material fromthe corn plant, such as corn cobs, corn plant husks and corn plantleaves and corn stalks (e.g. at least upper half or three-quartersportion of the stalk); the composition of the plant material (e.g.cellulose, hemicellulose and lignin) can be approximately as indicatedin FIG. 20A and FIG. 20B (e.g. after at least initial preparation of thebiomass, including removal of any foreign matter). According to anembodiment, the plant material comprises corn cobs, husks/leaves andstalks; for example, the plant material may comprise (by weight) up to100 percent cobs, up to 100 percent husks/leaves, approximately 50percent cobs and approximately 50 percent husks/leaves, approximately 30percent cobs and approximately 50 percent husks/leaves and approximately20 percent stalks, or any of a wide variety of other combinations ofcobs, husks/leaves and stalks from the corn plant. See FIG. 20A.According to an alternative embodiment, the lignocellulosic plantmaterial may comprise fiber from the corn kernel (e.g. in somecombination with other plant material). FIG. 20B provides typical andexpected ranges believed to be representative of the composition ofbiomass comprising lignocellulosic material from the corn plant.According to exemplary embodiments, the lignocellulosic plant materialof the biomass (from the corn plant) can comprise (by weight) celluloseat about 30 to about 55 percent, hemicellulose at about 20 to about 50percent, and lignin at about 10 to about 25 percent; according to aparticular embodiment, the lignocellulosic plant material of the biomass(e.g. cobs, husks/leaves and stalk portions from the corn plant) cancomprise (by weight) cellulose at about 35 to about 45 percent,hemicellulose at about 24 to about 42 percent, and lignin at about 12 toabout 20 percent. According to a particular embodiment, pre-treatment ofthe biomass can yield a liquid component that comprises (by weight)xylose at no less than approximately 1.0 percent and a solids componentthat comprises (by weight) cellulose (from which glucose can be madeavailable) at no less than around 45 percent.

FIG. 4 shows an apparatus 400 used for preparation, pre-treatment, andseparation of lignocellulosic biomass according to an exemplaryembodiment. As shown, biomass is prepared in a grinder 402 (e.g. agrinder or other suitable apparatus or mill). Pre-treatment of theprepared biomass is performed in a reaction vessel 404 (or set ofreaction vessels) supplied with prepared biomass, acid, and/or water ina predetermined concentration (or pH) and other operating conditions.The pre-treated biomass can be separated in a centrifuge 406 into aliquid component (C5 stream comprising primarily liquids with somesolids) and a solids component (C6 stream comprising liquids and solidssuch as lignin and cellulose from which glucose can be made available byfurther treatment).

According to an embodiment, in the pre-treatment system an acid can beapplied to the prepared biomass to facilitate the breakdown of thebiomass for separation into the liquid (pentose liquor) component (C5stream from which fermentable C5 sugars can be recovered) and the solidscomponent (C6 stream from which fermentable C6 sugars can be accessed).According to some embodiments, the acid can be applied to the biomass ina reaction vessel under determined operating conditions (e.g. acidconcentration, pH, temperature, time, pressure, solids loading, flowrate, supply of process water or steam, etc.) and the biomass can beagitated/mixed in the reaction vessel to facilitate the breakdown of thebiomass. According to exemplary embodiments, an acid such as sulfuricacid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, etc.(or a formulation/mixture of acids) can be applied to the biomass incombination with a xylose liquor recycle stream. The xylose liquorrecycle stream includes enzymes, acid, and water that may reduce therequirements for additional acid and water to be added at thepretreatment system. Maximization of sugar liberation and minimizationof inhibitor generation may be achieved by carefully controlling xyloserecycle volumes and process conditions. FIG. 23 provides theoreticalacid and water utilized for pretreatments dependent upon volume ofxylose liquor recycled during the pretreatment step. Additionally,economic data relating to the cost for the new acid is provided.Acid/Water usage was calculated for 10 pretreatment cycles using varyingamounts of recycled liquor. The calculations were based on 1000 kg ofcob at a 14.3% solids loading, using 1% H₂SO₄. Recycling a larger amountof xylose liquor into the next pretreatment results in a largerpercentage reduction in the amount of acid and water utilized insubsequent pretreatments. It was also found that by recycling liquorthere is an increase in the xylose concentration of the xylose liquorproportional to the amount of liquor being recycled. There is a maximumamount of liquor that can be recycled based on liquor availability dueto liquid solid separation efficiency and the amount of liquor takenfrom the process as a liquor stream. As illustrated, with larger volumesof xylose liquor recycle, water usage and acid addition decreasessignificantly. Up to around a 70% reduction in water and acid can beachieved, in some embodiments.

FIG. 5 illustrates an example graph 500 of the theoretical concentration502 for xylose in the xylose liquor stream for various recycle volumesover a number of cycles 504, according to an embodiment. The theoreticalxylose concentration was calculated for a xylose liquor recycle based ona 14.3% solids pretreatment with 100% xylose yield using cob with 32 gxylose per 100 g cob (e.g. 320 kg xylose per metric ton). The xyloseconcentration 502 was calculated by assuming 32 g of xylose in 700 g ofsolution from pretreatment, leading to a concentration of 4.57% for thefirst pretreatment. Then, an amount of liquor would be recycled into thenext pretreatment carrying with it a certain amount of xylose that wouldbe in addition to the amount of xylose produced during pretreatment of100 g cob (32 g xylose). With subsequent cycles, the xyloseconcentrations increased until the xylose concentrations leveled out ata steady state value. The larger the recycle volume, the more xylosethat is returned to the pretreatment, thereby further increasing theoutbound xylose concentration until saturation. For example, accordingto the theoretical values in FIG. 5, at a 70% xylose liquor recyclefinal xylose concentration after 20 cycles is estimated to reach about11.43% w/v.

In a similar manner, FIG. 6 illustrates an example graph 600 of thetheoretical concentration for acetic acid 602 (a fermentation inhibitorat some concentrations) in the xylose liquor stream for various recyclevolumes over a number of cycles 604, according to an aspect. Similarcondition assumptions to those used in FIG. 5 were used to model aceticacid concentrations. The first cycle, on average, produces an aceticacid concentration of about 6186 ppm. With subsequent cycles, the aceticacid concentrations increased until the acetic acid concentrationsleveled out at a steady state value. The larger the recycle volume, themore acetic acid that is returned to the pretreatment, thereby furtherincreasing the outbound acetic acid concentration until saturation. Forexample, according to the theoretical values in FIG. 6, at a 70% xyloseliquor recycle final acetic acid concentration after 16 cycles isestimated to reach about 15457 ppm.

According to a particular embodiment, sulfuric acid can be applied tothe biomass in pre-treatment in addition to the xylose liquor recyclestream. According to a particular embodiment, the prepared biomass maybe pretreated with approximately 0.8 to approximately 1.5 percent acid(such as sulfuric acid) and about 12 to about 25 percent biomass solidsat a temperature of approximately 100 to about 180 degrees Celsius forapproximately 5 to around 180 minutes. In alternate embodiments, xyloseliquor is supplied to the biomass at a set volume. The pH of the biomassis then adjusted to about 1.5 using concentrated acid, such as sulfuricacid. The use of a xylose recycle stream reduces the total new mineralacid that is needed to bring the pH to acceptable levels forpretreatment. The pre-treatment may also comprise a steam explosionstep, where biomass is heated to and held at (e.g. hold time)approximately 150 to approximately 165 degrees Celsius under pressure(e.g. 100 psi) at a pH of about 1.4 to about 1.6 for around 1 to around15 minutes, and the pressure is released to further aid in the breakdownof cellulose. After pretreatment the pre-treated biomass is separatedinto a solids component (C6) and a liquid pentose liquor component (C5),as shown in FIG. 4.

The liquid pentose liquor component (C5 stream) comprises water,dissolved sugars (such as xylose, arabinose, and glucose) to be madeavailable for fermentation into ethanol, acids, and other solublecomponents recovered from the hemicellulose. (FIG. 21B provides typicaland expected ranges believed to be representative of the composition ofbiomass comprising lignocellulosic material from the corn plant.)According to an exemplary embodiment, the liquid component may compriseapproximately 5 to approximately 7 percent solids (e.g.suspended/residual solids such as partially hydrolysed hemicellulose,cellulose, and lignin). According to a particular embodiment, the liquidcomponent comprises at least about 2 to about 4 percent xylose (byweight); according to other exemplary embodiments, the liquid componentcomprises no less than around 1 to around 2 percent xylose (by weight).FIG. 21A and FIG. 21B list the composition of the liquid component ofpre-treated biomass (from prepared biomass as indicated in FIG. 20A andFIG. 20B) according to exemplary and representative embodiments. Aportion of the C5 xylose liquid liquor stream may be recycled to thepretreatment as described above. In some embodiments, all (orsubstantially all) of the xylose liquor may be recycled. In theembodiments where all (or substantially all) of the xylose liquor is notrecycled the remaining xylose liquor that is not recycled may be treatedwith an alkali (such as sodium hydroxide, lime, or ammonium hydroxide)prior to being introduced to fermentation. Additional inhibitor removaltreatments may be performed on the xylose liquor, in some embodiments.

The solids component (C6 stream) comprises water, acids, and solids suchas cellulose from which sugar, such as glucose, can be made availablefor fermentation into ethanol and lignin. (FIG. 22B provides typical andexpected ranges believed to be representative of the composition ofbiomass comprising lignocellulosic material from the corn plant.)According to an exemplary embodiment, the solids component may compriseapproximately 10 to approximately 40 percent solids (by weight) (afterseparation); according to a particular embodiment, the solids componentcan comprise approximately 20 to approximately 30 percent solids (byweight). According to another embodiment, the solids in the solidscomponent comprise no less than about 30 percent cellulose and thesolids component may also comprise other dissolved sugars (e.g. glucoseand xylose). FIG. 22A and FIG. 22B list the composition of the solidscomponent of pre-treated biomass (from prepared biomass as indicated inFIG. 20A and FIG. 20B) according to exemplary and representativeembodiments.

After the separation of the C5 liquid component from the C6 solids, thesolids may be treated further in an enzymatic hydrolysis system.According to an embodiment, after pre-treatment, the solids component(C6) is supplied to a vessel for enzymatic hydrolysis (orsaccharification) along with enzymes, agents, and water. The enzymes canfacilitate the breakdown of pre-treated cellulose into sugar (e.g.glucose) to generate an enzymatic hydrolysis product. This sugar richenzymatic hydrolysis product may then be fermented into ethanol, or usedfor any other downstream process.

In some embodiments, the C6 solids may be subjected to a sequentialhydrolysis and fermentation (SHF) process, wherein the solids aresubjected to an enzyme hydrolysis (with a glucan conversion of at least80%) followed by a fermentation. While using a two-step process, withthe SHF approach enzyme hydrolysis may be performed at optimal pH (or asnear an optimal pH as possible) and temperature for conversion ofcellulose to sugars. For SHF, the solids are treated at about 50° C.,around 5.5 pH, and about 15% total solids slurry with cellulase.

Alternatively, the C6 solids may be subjected to a simultaneous (oralmost simultaneous) saccharification and fermentation (SSF) processwherein the enzyme hydrolysis and fermentation is performed at about thesame time. Simultaneous (or near simultaneous) saccharification andfermentation can be performed at temperatures suitable for ethanolproduction by the yeast (e.g., about 37° C.) which can be less thanoptimal for the cellulase enzyme, according to an aspect.

According to an exemplary embodiment, an enzyme formulation comprisingan enzyme capable of hydrolysing cellulose is supplied to the solidscomponent (C6) to facilitate the enzyme hydrolysis, e.g. thesaccharification by enzyme action of the polymeric cellulose (e.g.polymeric glucan) into accessible monomeric sugars (e.g. monomericglucose). An example of such cellulase enzyme is Cellic CTec (e.g.NS22074) from Novozymes North America, Inc. of Franklinton, N.C. Theamount or loading (dose) of enzyme formulation may be varied as anoperating condition. According to an exemplary embodiment, approximately2 to approximately 12 milligrams of enzyme protein per gram of cellulosemay be added. According to a particular embodiment, approximately 3 toapproximately 9 milligrams of enzyme protein per gram of cellulose maybe added.

According to an exemplary embodiment, the temperature during thetreatment of the solids component (C6) may be approximately 30 toapproximately 60 degrees Celsius. According to an embodiment, thetemperature during the treatment of the solids component (C6) may beapproximately 45 to approximately 55 degrees Celsius, and according to aparticular embodiment, the temperature during the treatment of thesolids component (C6) may be approximately 49 to around 51 degreesCelsius.

According to an exemplary embodiment, the treatment time of the solidscomponent (C6) may be approximately 48 to about 144 hours. According toan embodiment, the treatment time of the solids component (C6) may beapproximately 60 to approximately 120 hours, and according to aparticular embodiment, the treatment time of the solids component (C6)may be around 72 to about 96 hours.

According to an exemplary embodiment, the solids content of the solidscomponent (C6) supplied to the treatment system may be approximately 5to approximately 25 percent by weight. According to an embodiment, thesolids content of the solids component (C6) may be approximately 10 toapproximately 20 percent by weight, and according to a particularembodiment, the solids content of the solids component (C6) may beapproximately 12 to approximately 17 percent by weight.

According to an exemplary embodiment, the pH during the treatment of thesolids component (C6) may be approximately 4.8 to about 6.2. Accordingto an embodiment, the pH during the treatment of the solids component(C6) may be approximately 5.2 to around 5.8, and according to aparticular embodiment, the pH during the treatment of the solidscomponent (C6) may be approximately 5.4 to approximately 5.6.

A glucose yield that may be achieved during enzyme hydrolysis of biomass(e.g. corn cobs, husks, leaves and/or stalks) using available cellulaseenzymes without the addition of thin stillage, clarified thin stillage,or anaerobic membrane bioreactor effluent may be in the range of around35 to around 40 percent of theoretical (e.g. calculated) glucose yieldfor simultaneous (or almost simultaneous) saccharification andfermentation (SSF) and between about 55 to about 70 percent oftheoretical glucose yield for sequential hydrolysis and fermentation(SHF). Exact glucose yields may vary dependent upon pretreatmentprocedures. For example, inclusion of steam explosion pretreatment, asdescribed above, may increase glucose conversion yields for SHFprocessed biomass.

As discussed herein, an aspect relates to a method for pretreatinglignocellulosic biomass. The method can include applying an acidsolution to a first portion of biomass and maintaining an elevatedtemperature of the first portion of biomass such that a xylose yield ofgreater than about 80% of theoretical is achieved. A liquid xyloseliquor and a glucan solid are produced from the first portion of biomasswhile maintaining the elevated temperature. The method can also includeseparating at least a portion of the liquid xylose liquor from theglucan solid, applying the portion of the liquid xylose liquor to asubsequent portion of the biomass, and applying a makeup acid solutionto the subsequent portion of the biomass. Further, the method caninclude maintaining an elevated temperature of the subsequent portion ofthe biomass such that xylose yield of greater than about 80% oftheoretical is achieved. A liquid xylose liquor and a glucan solid areproduced from the subsequent portion of the biomass while maintainingthe elevated temperature. The method can repeat starting with separatingthe portion of the liquid xylose liquor to a subsequent portion of thebiomass. In some implementations, the method can include releasing sugarglucose.

In an example, maintaining the elevated temperature can includemaintaining the temperature at about 120° C. and 150° C. In anotherexample, maintaining the elevated temperature can include maintainingthe elevated temperature for at least about 10 minutes. In a furtherexample, maintaining the elevated temperature can include maintainingthe elevated temperature for less than about 120 minutes.

In some implementations, applying the acid solution can include applyingan acid solution that is between about 1% to 1.6% sulfuric acid. In someimplementations, the elevated temperature of the first portion ofbiomass and the elevated temperature of the subsequent portion of thebiomass can be maintained until greater than about 90% of theoreticalxylose yield is achieved. In other implementations, the elevatedtemperature of the first portion of biomass and the elevated temperatureof the subsequent portion of the biomass can be maintained until greaterthan about 45% of theoretical glucose yield is achieved. In someimplementations, the elevated temperature of the first portion ofbiomass and the elevated temperature of the subsequent portion of thebiomass can be maintained until greater than about 50% of theoreticalglucose yield is achieved.

In an aspect, the liquid xylose liquor comprises less than about 4000ppm furfural. In some aspects, the liquid xylose liquor comprises lessthan about 3000 ppm furfural. According to some aspects, the portion ofthe liquid xylose liquor is about 70% of the total xylose liquor.According to other aspects, the portion of the liquid xylose liquor isabout 75% of the total xylose liquor.

Another aspect relates to a method for pretreating lignocellulosicbiomass to be supplied to a fermentation system for production of afermentation product. The method can include applying a xylose liquor tobiomass, applying a makeup acid solution to the biomass, and maintainingan elevated temperature of the biomass such that a xylose yield ofgreater than about 80% of theoretical is achieved. Xylose liquor and aglucan solid can be produced from the biomass while maintaining theelevated temperature. The method can also include separating at leastsome portion of the xylose liquor from the glucan solid. The method canrepeat with applying an acid solution to the biomass.

EXAMPLES

A series of limited examples were conducted according to an exemplaryembodiment of the system in an effort to evaluate the effect of varyingrecycle volumes and process conditions. Experiments and tests wereconducted to evaluate xylose concentrations, glucose yields, acetic acidconcentrations, and inhibitor levels (such as furfural) as a function ofrecycle volume, cycle number, and process conditions. The followingexamples are intended to provide clarity to some embodiments of systemsand means of operation and are not intended to limit the scope of thevarious aspects disclosed herein.

FIG. 24 provides an overview of the example experimental conditions,including pretreatment temperature, cycle numbers, sulfuric acidconcentration, and timing. For all examples, sugar,furfural/5-hydroxy-methylfurfural (HMF), and acetic acid levels weremeasured utilizing known HPLC (High-Performance Liquid Chromatography)analytical techniques. Glucose concentrations were measured after asaccharification step. Further, pretreatment makeup was adjusted formoisture variability of the ground biomass samples. For each examplecondition, all (or substantially all) pretreatment liquor was used torecycle to the next cycle (excluding a small test volume for analytics).

For all examples, cob material was hammer milled and stored in a Quonsetbut style building to maintain a dry environment with minimal or noexposure to the sun and inclement weather. Sulfuric acid was obtainedfrom Fisher Scientific (of Waltham, Mass.) in reagent form for theBabcock Milk Test SA174-4 91.6% acid.

The ground cob was used to make a 14.3% solids solution with acidsolution containing the prescribed concentration of acid for thepretreatment conditions as presented in FIG. 24. The 1 L Parr reactorvessel was loaded with 100 g of ground cob on a dry weight basis; waterand sulfuric acid were combined to achieve the desired acidconcentration in the liquid fraction while accounting for water broughtin with the biomass and then added to the raw biomass. The acid solutionand cobs were stirred with a spatula to wet the entire sample. Thevessel was then connected to the Parr reactor head and stirred at 450rpm. Heat was applied by supplying high pressure steam (250 to 300 psi)into the vessel jacket. The temperature was monitored using athermocouple in the external thermowell. The heat was adjustedaccordingly by adding either steam or cold water to the vessel jacket.The reaction timer started as soon as the vessel contents reached thedesired temperatures. After the vessel had been held at temperature forthe appropriate amount of time, the vessel was cooled using waterthrough the vessel jacket.

After the reaction was complete, the Parr reactor vessel was removed andthe pretreatment slurry was transferred into a tared 1000 mlpolypropylene centrifuge tube. The slurry was then separated viacentrifuge at 4500 rpm for 15 minutes. The moisture level of the solidswas determined using an oven moisture procedure, and then submitted forenzymatic saccharification. A 30 g sample of the xylose liquor was takenfor sugar (xylose, glucose, and arabinose), HMF, Furfural, acetic acid,and total solids (dissolved and suspended) analysis. The remaining massof liquor was used as recycle liquid for the next pretreatment.

Subsequently, the solids were diluted to 10% with water. Hydrolysis wasperformed in 125 ml Erlenmeyer flasks with 70 ml of slurry. The slurriesin each flask were pH adjusted to 5.5 using 45% w/w aqueous potassiumhydroxide or 10% v/v aqueous sulfuric acid. Enzyme loadings were 9 mgenzyme protein per g glucan (the glucan content of the solids portionwas assumed as 35%). The flasks were incubated in a water bath shaker at50° C. (stirred at 150 rpm) for 72/96 hours.

The recycle process was performed by loading the Parr reactor vesselwith 100 g ground cob on a dry weight basis, the recycle liquid from theprevious pretreatment was added, the reaction mass was adjusted to 700 gusing a dilute acid solution with appropriate acid concentration fromFIG. 24. The process for pretreatment was then carried out identically(or nearly identically) for each recycle step. This recycle process wasrepeated for the number of times designated in the experimental design.

In the example experiment, xylose concentration, glucose concentration,and acetic acid concentration for each of the conditions illustrated inTABLE 5 were analyzed. Xylose liquor was collected and filtered througha 0.2 μm syringe into HPLC vials. The vials were then loaded onto acarousel, which fits into an auto sampler (either 717 plus or 2659separations module from Waters of Milford, Mass.). An aliquot (5 μl) ofthe sample was injected by the auto-injector onto a reverse phase column(HPX-87H from Bio-Rad Laboratories of Hercules, Calif.) maintained at50° C. Sulfuric acid at 0.005M was used as the mobile phase (eluent).The HPLC system was equipped with a refractive index detector (eitherthe 2410 or 2414 model from Waters). The components (sugars, organicacids, and ethanol) were identified and quantified using the Empowersoftware (Waters).

Furfural and HMF concentration for each of the conditions illustrated atFIG. 24 were analyzed. Samples were prepared by diluting the xyloseliquor tenfold with water and filtering through a 0.2 μm nylon syringefilter into HPLC vials. A 10 μl aliquot was injected by the HPLCautosampler (Dionex Ultimate 3000) onto a reversed phase HPLC C18 columnat 40° C. The samples were eluted with a mobile phase consisting of asolution of 90:5:5 water:acetonitrile:methanol at a flow rate of 1ml/min. Furfural and HMF were detected by UV at 280 nm wavelength. Lateeluting compounds were washed off the column by a column wash mobilephase consisting of 50:10:40 water:acetonitirle:methanol at 1 ml/ml for5 min.

Results for the analysis of xylose as a function of number of recyclesare illustrated in the graphs of FIGS. 7-10. In particular, FIG. 7illustrates an example graph 700 of the percent xylose yields 702 forthe samples treated at 120° C. for 120 minutes at varying acid solutionsfor different cycles 704 (as detailed in FIG. 24). FIG. 8 illustrates anexample graph 800 of the percent xylose yields 802 for the samplestreated at 140° C. for 20 minutes at varying acid solutions for a numberof different cycles 804 (as detailed in FIG. 24). FIG. 9 illustrates anexample graph 900 of the percent xylose yields 902 for the samplestreated with a 1% acid solution at varying times and temperatures over anumber of different cycles 904 (as detailed in FIG. 24). FIG. 10illustrates an example graph 1000 of the percent xylose (w/v) 1002 inthe pretreatment liquor as a function of recycle numbers 1004. Asillustrated, xylose concentrations increase as recycle numbers increaseuntil a steady state concentration is reached. In this exampleembodiment, the greatest overall xylose yield was achieved using a 10minute pretreatment with 1% acid solution and 150° C. temperature.

Results for the analysis of glucose as a function of number of recyclesare illustrated in the graphs of FIGS. 11-13. In particular, FIG. 11illustrates an example graph 1100 of percent glucose yields 1102 for thesamples treated at 120° C. for 120 minutes at varying acid solutions asa function of recycle numbers 1104 (as detailed in FIG. 24). FIG. 12illustrates an example graph 1200 of percent glucose yields 1202 for thesamples treated at 140° C. for 20 minutes at varying acid solutions as afunction of recycle numbers 1204 (as detailed in FIG. 24). FIG. 13illustrates an example graph 1300 of percent glucose yields 1302 for thesamples treated at 150° C. for 10 minutes with a 1% acid solution asfunction of recycle numbers 1304 (as detailed in FIG. 24). Asillustrated, glucose yields increase with each recycle at the 120° C.conditions. However, at 140° C. conditions and 150° C. condition,glucose yields are variable over the successive recycles.

Results for the analysis of acetic acid as a function of number ofrecycles are illustrated in the graphs of FIGS. 14-16. In particular,FIG. 14 illustrates an example graph 1400 of percent acetic acid yields1402 for the samples treated at 120° C. for 120 minutes at varying acidsolutions as a function of recycle numbers 1404 (as detailed in FIG.24). FIG. 15 illustrates an example graph 1500 of percent acetic acidyields 1502 for the samples treated at 140° C. for 20 minutes at varyingacid solutions, as a function of recycle numbers 1504 (as detailed inFIG. 24). FIG. 16 illustrates an example graph 1600 of acetic acidconcentrations 1602 for the samples treated at 150° C. for 10 minutesand 130° C. for 60 minutes, both with a 1% acid solution, as a functionof recycle numbers 1604 (as detailed in FIG. 24). As illustrated, aceticacid concentrations increase as recycle numbers increase. Yields ofacetic acid remain relatively consistent (as a percentage) over thesuccessive recycles. Higher acid concentration tends to result in higheracetic acid formation, likely due to treatment severity.

Results for the analysis of furfural as a function of number of recyclesare illustrated in the graphs of FIGS. 17-19. In particular, FIG. 17illustrates an example graph 1700 of furfural concentration 1702 for thesamples treated at 120° C. for 120 minutes at varying acid solutions asa function of recycle numbers 1704 (as detailed in FIG. 24). FIG. 18illustrates an example graph 1800 of percent furfural concentration 1802for the samples treated at 140° C. for 20 minutes at varying acidsolutions as a function of recycle number 1804 (as detailed in FIG. 24).FIG. 19 illustrates an example graph 1900 of furfural concentration 1902for the samples treated at 150° C. for 10 minutes and 130° C. for 60minutes, both with a 1% acid solution as a function of recycle numbers1904 (as detailed in FIG. 24). As illustrated, furfural concentrationsincrease with each recycle at all conditions. Further, the level offurfural is much higher for the 1.6% acid compared to the 1% acidloading. The decreasing yields at 1% acid and the increasing yields at1.6% acid tend to indicate a decreasing severity in the pretreatment asthe xylose liquor is recycled at 1% acid and an increasing severity at1.6% acid. This is likely a result of the slightly higher acetic acidbeing produced and the elevated levels of acid catalyst.

FIG. 25 summarizes the experimental data in tabular format. The 1% acid,120° C., 2 hour xylose liquor recycle pretreatments resulted in xyloseyields of 85-100% and glucose yields of 45-55% (from low enzyme dosing).When a 1.2% sulfuric acid was used the highest xylose yields occurred.In contrast, 1% acid yielded the highest glucose levels. Xylose yieldsbetween 90 and 100% are achieved with 1.6% acid loading. Acetic acidyields show the same trends for the 1% acid pretreatments at around80-85% and the 1.6% acid pretreatments from 85-95% as compared to xyloseyields. Glucose yields are between 45% and 65% with the 1.6% acidloading showing an upward trend over the 5 pretreatment cyclesincreasing from about 55-65% while the 1% actually seems to cause adecrease in glucose yield as it is recycled.

The 150° C. xylose liquor recycle pretreatments have xylose yieldsapproaching 100% and glucose yields that start near 60% but then falloff to reach a steady state in the 50% range, the pretreatment alsoproduces around 85-90% of the theoretical acetic acid available.

The 130° C. pretreatments have xylose yields in the 90-95% range thatshows a decreasing yield as recycles progress, the same trend is seen inthe acetic acid yield. The elevation in temperature from 130° C. to 150°C. causes an increased amount of xylose being converted to furfural.These trends in sugar, acetic acid, and furfural production support theassessment that 150° C. at the same acid level provides higherpretreatment severity than 130° C. for longer periods of time (10minutes versus 60 minutes).

When the xylose yield trends are examined across the entire experimentaldesign, the 1% acid recycles have a downward trend suggesting that thereis not enough acid being recycled with the xylose liquor to maintain theseverity level. Conversely, the 1.6% acid data shows an increase in bothxylose and glucose yield which indicates that there is an increase inseverity that leads to a higher yield pretreatment, possibly due toincreasing levels of acetic acid. The 1.2% and 1.4% acid yield forxylose and glucose remain relatively steady.

The embodiments as disclosed and described in the application (includingthe FIGURES and Examples) are intended to be illustrative andexplanatory of the present inventions. Modifications and variations ofthe disclosed embodiments, for example, of the apparatus and processesemployed (or to be employed) as well as of the compositions andtreatments used (or to be used), are possible; all such modificationsand variations are intended to be within the scope of the presentinventions.

The word “exemplary” is used to mean serving as an example, instance, orillustration. Any embodiment or design described as “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or designs, nor is it meant to preclude equivalent exemplarystructures and techniques known to those of ordinary skill in the art.Rather, use of the word exemplary is intended to present concepts in aconcrete fashion, and the disclosed subject matter is not limited bysuch examples.

The term “or” is intended to mean an inclusive “or” rather than anexclusive “or.” To the extent that the terms “comprises,” “has,”“contains,” and other similar words are used in either the detaileddescription or the claims, for the avoidance of doubt, such terms areintended to be inclusive in a manner similar to the term “comprising” asan open transition word without precluding any additional or otherelements.

What is claimed is:
 1. A method for pretreating lignocellulosic biomass,comprising: a) applying an acid solution to a first portion of biomassfeedstock, wherein the biomass feedstock comprises ground corn cobs andcorn stover, and wherein the acid solution comprises between about 1% to1.6% sulfuric acid; b) maintaining an elevated temperature of the firstportion of biomass feedstock to hydrolyze hemicellulose present in thebiomass feedstock such that a xylose yield of greater than about 80% oftheoretical is achieved, wherein a liquid xylose liquor comprisingfurfural in an amount of 4000 ppm or less and a glucan solid areproduced from the first portion of biomass feedstock while maintainingthe elevated temperature, wherein the maintaining the elevatedtemperature comprises maintaining the elevated temperature within therange of about 120° C. to 150° C.; c) before step “h”, separating atleast a portion of the liquid xylose liquor from the glucan solid; d)recycling a fraction of liquid xylose liquor that is separated from theglucan solid and applying the fraction of the liquid xylose liquor to asubsequent portion of the biomass feedstock, wherein the fraction of theliquid xylose liquor that is recycled is 70% or more of the total xyloseliquor that is separated from the glucan solid; e) applying a makeupacid solution to the subsequent portion of the biomass feedstock; f)maintaining an elevated temperature of the subsequent portion of thebiomass feedstock such that xylose yield of greater than about 80% oftheoretical is achieved, wherein a liquid xylose liquor and a glucansolid are produced from the subsequent portion of the biomass feedstockwhile maintaining the elevated temperature, wherein the maintaining theelevated temperature comprises maintaining the elevated temperaturewithin the range of about 120° C. to 150° C.; g) repeating steps c)through f) at least three times; and h) enzymatically hydrolyzing theglucan solid to produce glucose.
 2. The method of claim 1, furthercomprising releasing sugar glucose.
 3. The method of claim 2, wherein atstep b) and step f) greater than about 45% of theoretical glucose yieldis achieved.
 4. The method of claim 2, wherein at step b) and step f)greater than about 50% of theoretical glucose yield is achieved.
 5. Themethod of claim 1, wherein the maintaining the elevated temperaturecomprises maintaining the elevated temperature for at least about 10minutes.
 6. The method of claim 1, wherein the maintaining the elevatedtemperature comprises maintaining the elevated temperature for less thanabout 120 minutes.
 7. The method of claim 1, wherein at step b) and stepf) greater than about 90% of theoretical xylose yield is achieved. 8.The method of claim 1, wherein the liquid xylose liquor comprises lessthan about 3000 ppm furfural.
 9. The method of claim 1, wherein step g)is repeated at least five times.
 10. The method of claim 1, wherein stepg) is repeated for about ten cycles.
 11. A method for pretreatinglignocellulosic biomass to be supplied to a fermentation system forproduction of a fermentation product, comprising: a) applying a xyloseliquor to biomass feedstock, wherein the biomass feedstock comprisesground corn cobs and corn stover; b) applying a makeup acid solution tothe biomass feedstock; c) maintaining an elevated temperature of thebiomass feedstock to hydrolyze hemicellulose present in the biomassfeedstock such that a xylose yield of greater than about 80% oftheoretical is achieved, wherein xylose liquor comprising furfural in anamount of 4000 ppm or less and a glucan solid are produced from thebiomass feedstock while maintaining the elevated temperature, whereinthe maintaining the elevated temperature comprises maintaining theelevated temperature within the range of about 120° C. to 150° C.; d)before step “f”, separating at least some portion of the xylose liquorfrom the glucan solid, and recycling a fraction of liquid xylose liquorthat is separated from the glucan solid and applying the fraction of theliquid xylose liquor to a subsequent portion of the biomass feedstock,wherein the fraction of the liquid xylose liquor that is recycled is 70%or more of the total xylose liquor that is separated from the glucansolid; e) repeating steps a) through d) at least three times; and f)enzymatically hydrolyzing the glucan solid.